Natural history of early diabetic nephropathy: What are the effects of therapeutic intervention?

Several studies have shown that lowering of blood pressure slows the rate of progression of diabetic renal disease. Some placebo-controlled studies have also shown that angiotensin-converting enzyme (ACE) inhibitors decrease or stabilize albuminuria in incipient nephropathy and slow the rate of progression of advanced nephropathy. However, it is not yet clear if prolonged treatment with ACE inhibitors or with other agents exerts a specific renoprotective effect in incipient diabetic nephropathy. It is proposed that such an effect should be independent from changes in systemic blood pressure and should be characterized by amelioration of the rate of rise of albumin excretion rate (AER) and the rate of fall of glomerular filtration rate (GFR) and independence from changes in other parameters known to influence AER (glycemic control, protein intake, sodium intake). In addition, there should be evidence that the potentially reversible effects of therapeutic intervention on AER and GFR are translated to long-term changes in renal function and structure. This paper reviews the evidence on which the concept of renoprotection is based, with particular reference to choice of end points, heterogeneity of study groups, and complexities of the disease process, and relates this evidence to the natural history of nephropathy in type I and type II diabetes. Based on the above, an assessment is made of the comparative effects of ACE inhibitors and other antihypertensive agents on AER and GFR. It is suggested that longitudinal intra-individual analysis of both variables may be necessary in order to determine whether ACE inhibitors exert greater renoprotection than calcium channel blockers or other antihypertensive agents.